The present invention relates in general to an apparatus for improving combustion efficiency of a rotary kiln. For example, a rotary kiln for sintering cement is provided with a burner or burners for heavy oil, pulverized coal or for both of them at the fore end thereof to allow fuel to inject into the rotary kiln.
If the primary air is supplied after it is preheated to a high temperature and under a high pressure, any fuel is smoothly ignited and burned. Secondary, air is supplied to a clinker box as cooling air and is in contact with clinker in the clinker box, thus the said cooling air is elevated to a high temperature near 1000.degree. C.; this high temperature air is allowed to be supplied from the periphery of the said burner.
If the primary air is excessive, the secondary air is inevitably reduced. As a result, the latter is further preheated by the clinker, which will damage the clinker box as well as decrease the overall combustion efficiency.
The present invention is therefore, how to reduce a primary air rate and how to prevent the clinker box from damage.